David Marsh, who wrote it, adds in the comments part:
Since you have done this twice now
If you consult a proper English grammar (i.e. written by a linguist, as opposed to a style guide written by someone with no training in linguistics, masquerading as a grammar) ...
I’ve got a master’s in English language and linguistics from UCL (where among others I learned from Quirk himself, as well as Quirk et al).
With a few exceptions such as David Crystal and Steven Pinker, most linguists can’t write for toffee, which is why Bill Bryson and Lynne Truss have done so well for themselves in this area.
As an editor and journalist I’m trying to help my colleagues, and our readers, to communicate clearly and coherently.
For the record, the Guardian’s is the least prescriptivist style guide on the planet and defines grammar (which I do not mention once in the blogpost, incidentally) like this:
Nowadays, grammar might be more helpfully defined as the set of rules followed by speakers of a language: for example, why in English we say “I went out” and not “I out went”. Using correct grammar is a way to communicate effectively, not to feel superior to other people because you know what a conjunction is.
Don’t feel too downhearted if you were taught grammar badly, or not at all; as the linguist Steven Pinker says: “A preschooler’s tacit knowledge of grammar is more sophisticated than the thickest style manual”.